While you can activate this mission without penalty, completing it by defeating the boss in Sioran Crypt will effectively deny you training and a side mission, On the Hunt if you have not completed those tasks yet.

Head out to the area to the east of Meathgra's Den in The Midden to get started. Follow the Delver to her spot, then defend her from the wild Fae (enemy ambush).

Once the Delver is done scrying, she will point you to the next place Sioran Crypt in the Drowned Forest. Head there and look for the suspected Tuatha spy, Cadoroc. Kill him (stealth kills work) and his pet spiders, and return to Bisarane.

Only, you can't. Taibreah will meet you at the entrance to the House of Sorrows and tell you about some Fae rebellion. Your reply will not change how you get back into the House of Sorrows to see Bisarane; once you reply, you effectively finish this quest and move on to A House Divided.